1. Field of the Invention
The present invention relates to a disk drive, and more particularly, to a disk drive which can reduce vibration generated by rotation of a disk.
2. Description of the Related Art
In general, disk drives are used to record information on a disk shaped medium, such as a compact disk (CD) or a digital video disk (DVD), or reproduce the information recorded on the medium.
FIG. 1 shows an example of a typical disk drive. As shown in the drawing, a disk drive includes a frame 20 installed in a housing 10, a spindle motor 30 installed on the frame 20 to rotate a disk D, a turntable 40 coupled to a rotation shaft of the spindle motor 30 and on which the disk D is placed, and a pickup unit 50 reciprocating in a radial direction of the rotating disk D to record or reproduce information.
In the disk drive having the above structure, while the disk D is rotated, the pickup unit 50 records information on a recording surface of the disk D or reproduces the information recorded on the recording surface.
Preferably, the disk D used in the disk drive is completely flat and has a uniform mass distribution. However, it is practically impossible to make such a disk, and a general disk has warp and irregular mass distribution as shown in FIG. 2. referring to FIG. 2, a value obtained by multiplying mass m by distance r from the center of the disk D is eccentric mass m′, which quantitatively represents irregularity of mass distribution of the disk D. Gram·centimeter (g·cm) is used as a unit for eccentric mass m′.
When the disk D having the eccentric mass m′ and warp is placed on the turntable 40 and rotated at a high speed by the spindle motor 30, an exciting force in a horizontal direction proportional to the eccentric mass m′ and an exciting force in a vertical direction proportional to the amount of warp are generated, so that the frame 20 is vibrated. Typically, the vibrations are not completely alleviated by buffer members 60 installed at coupling portions P1, P2, P3 where the frame 20 and the housing 10 are coupled.
Recently, to solve the above problem, a disk drive adopting a ball balancer has been suggested, as shown in FIG. 3. The ball balancer includes a circular accommodation portion 70 formed on the turntable 40, and a plurality of balls 80 rotating in the accommodation portion 70. In this structure, when a disk having an eccentric mass m′ is placed on the turntable 40 and rotated, the balls 80 are disposed at a position opposite to the eccentric mass m′ in the accommodation portion 70, according to the principle of rotor dynamics, to maintain balance in mass, so that vibration generated due to the eccentricity of the disk can be reduced.
The ball balancer can provide a good vibration reduction effect at high disk speeds. But at low speeds, since the balls 80 are gathered toward the eccentric mass m′, vibration and noise are increased. With the ball balancer, in general, when information is recorded on a disk, since the disk is driven at low speeds, a recording error may be made due to the effect of the ball balancer.
Also, the ball balancer reduces vibration in the horizontal direction generated due to the eccentric mass m′, but has no effect on the vibration in the vertical direction generated due to a disk warp.
When the frame 20 is vibrated by the exciting force in the horizontal and vertical directions generated due to the eccentric mass m′ and a warp of the disk D, accurate position control in the vertical and horizontal directions between the disk D and the pickup unit 50 is difficult. Thus, the vibration in the frame 20 prevents a disk from having an increased recording density of a disk, and therefore a large capacity. The vibration also prevents high speed recording and reproduction of the disk.